1. Field of the Invention
The present invention relates to method and apparatus for correcting a concentration and, more particularly, to the improvement of a mechanism of correcting the measured concentration of a sample the volume of which varies with a pressure and a temperature.
2. Description of the Related Art
Optical means for measuring a predetermined ingredient in a liquid or a gas have found spreading use and, in particular, the absorbance measurement method is generally adopted for the measurement of concentration because it does not require complicated operation.
In the absorbance measurement method, the absorbance of a sample is measured, and the measured value is substituted into the preset equation of a calibration curve to obtain the concentration of the sample. This is based on the fact that the absorbance of the sample is dependent on the quantity (concentration) of a material being measured which is contained in a predetermined volume of the sample on the assumption that the volume of the sample does not change under any condition.
In the case of measuring an ingredient which is contained in a refrigerant such as flourocarbon and liquified carbon dioxide gas, however, the volume of such a medium varies with a pressure, temperature, etc., and the content of the material being measured per volume also varies with the change.
As a result, the concentration of the material per volume obtained is not proportional to the content per weight, which is required as a more substantial quantity, and it is impossible to obtain the accurate concentration per unit weight.
If a sample is measured under strictly constant pressure and temperature, this problem is solved. In order to realize this measurement, however, very strictly and complicated control of the measuring system is necessary. In addition, since the measuring conditions are different in apparatuses and measured absorbances, the objectivity of the measured data on the concentration of the material can not be expected.